(a) Field of Invention
The present invention relates generally to luminaires which are mountable on vertical surfaces. More specifically the invention relates to a panel-mounted luminaire, such as those used with partition panels in modular office furniture systems, where the luminaire is configured to reduce excessive luminance on the vertical surface while still providing sufficient luminance to said vertical surface and/or an associated worksurface.
(b) Description of Related Art
Luminaires are often used in conjunction with conventional modular office furniture systems. Such luminaires may be task lights that direct their output in a downward direction only to illuminate worksurfaces located below the luminaires, ambient lights that direct their output in an upward direction only to illuminate ceilings and give general lighting to the space, or task/ambient luminaires that provide both downward and upward directed light. These luminaires are often fashioned as elongated units suitable for use with linear type fluorescent lamps and are capable of providing broad areas of lighting for horizontal worksurfaces and associated partition panels.
Workstation integrated task and task-ambient luminaires are well known in the industry and are especially effective at achieving quality task illumination in open office environments. Generally, such luminaires are configured to mount on open office workstation partitions, walls, or, as may be the case with those that provide only downward task lighting, to an underside of workstation shelves or elevated storage cabinets (also known as “binder bins”).
Linear type fluorescent lamps of nominal 1″ diameter (T8) or ⅝″ diameter (T5) are the most popular lamps for applications involving these task and task-ambient luminaires. Consequently, installations typically consist of luminaires ranging from 2 feet in length to as much as 8 feet in length, each incorporating 2′, 3′, 4′, or 5′ long fluorescent lamps singly or in tandem as dictated by the length of the unit. Common desirable mounting practices typically position the luminaires slightly above seated eye height and coincident to a primary task area of a worksurface generally disposed horizontally some distance beneath the mounted task luminaire. Worksurfaces that are 24 to 30 inches deep (front to back) and 6 to 8 feet long are common and are desirably served by task lighting that extends nearly or completely over an entire length of the worksurface, thus providing broad and relatively uniform areas of task lighting within the workstation.
In addition to lighting the requisite horizontal worksurface, much effort is often taken in the design of such luminaires to similarly illuminate the vertical surface that typically extends upwardly from the edge of the worksurface opposite from the viewer. This vertical surface may be a wall, a privacy partition panel, etc. These efforts are generally directed at alleviating shadowing of overhead ambient lighting by said luminaire, shelf and/or binder bin in an attempt to create a balanced luminous surround for vertically oriented visual tasks (such as VDT viewing) in addition to traditional paper tasks.
Specifically, a desirable visual balance may be achieved when the luminance ratio between a task and the immediately adjacent surroundings (workstation surfaces) does not exceed 3:1 or 1:3. (ref: ANSI/IESNA RP-1-04 American National Standard for Office Lighting). Thus, for the typical VDT screen with an average luminance of 90 candelas per square meter (cd/m2), the vertical workstation panel(s) adjacent to said VDT should have a luminance in the range of 30 to 270 cd/m2. The industry Standards further recommend that such panels have a reflectance of 40% to 70% and be non-specular (i.e. diffuse). Therefore, such luminances are typically realized when such workstation panels are illuminated to 22 to 114 footcandles. However, current task-oriented workstation luminaires often do not provide this luminance balance, thus resulting in visual fatigue and discomfort to the viewer as the worker's eye repeatedly adjusts to disparate luminances in the field of view. Such visual fatigue and discomfort is known to diminish the productivity of the affected worker in performing workstation tasks.
Furthermore, in using such task oriented workstation luminaires, it is often desirable to achieve a narrow profile, i.e., a narrow outward extension from the vertical surface, in order to: (1) achieve a spacious and open feeling workstation; (2) minimize any shadow the luminaire might cast on workstation surfaces due to overhead ambient lighting; (3) minimize any asymmetric weight load/moment on the supporting panel and/or brackets; and (4) minimize fabrication costs associated with larger luminaire units. However, a task luminaire having a smaller cross-section and a corresponding reduced extension from the vertical surface generally places the lamp closer to the vertical surface thus causing luminance of the vertical surface proximate to the aperture to exceed the recommended limits.
Therefore, a luminaire is desired that overcomes these disadvantages and offers improved luminance distribution across a vertical mounting surface and an associated worksurface. Specifically, a luminaire is desired having a lamp distribution modifying feature which reduces luminance on the vertical mounting surface proximate to the luminaire while maintaining sufficient luminance on areas of the mounting surface disposed distally relative to the luminaire and across the associated worksurface, where such feature is discrete so as not to detract from the aesthetics of the luminaire, and where such feature is cost-effectiveness, easy to install, and capable of retrofit and reposition.